The form of leaven used in bread-making and the method of using it were simple and definite. The "leaven" consisted always, so far as the evidence goes, of a piece of fermented dough kept over from a former baking. There is no trace of the use of other sorts of leaven, such as the lees of wine or those mentioned by Pliny (NH, xviii.26). The lump of dough thus preserved was either dissolved in water in the kneading-trough before the flour was added, or was "hid" in the flour (the King James Version "meal") and kneaded along with it, as was the case mentioned in the parable (Matthew 13:33). The bread thus made was known as "leavened," as distinguished from "unleavened" bread (Exodus 12:15, etc.).

See BREAD.

(2) In Law and Ritual.

The ritual prohibition of leaven during "the feast of unleavened bread" including the Passover (Exodus 23:15, etc.) is a matter inviting restudy. For the historical explanation given in the Scriptures, see especially Exodus 12:34-39; 13:3; Deuteronomy 16:3. The antiquity of the prohibition is witnessed by its occurrence in the earliest legislation (Exodus 23:18; 34:25). A natural reason for the prohibition, like that of the similar exclusion of honey, is sought on the ground that fermentation implied a process of corruption. Plutarch voices this ancient view of the matter when he speaks of it as "itself the offspring of corruption, and corrupting the mass of dough with which it is mixed." Fermentatum is used in Persius (Sat., i.24) for "corruption." For this reason doubtless it was excluded also from the offerings placed upon the altar of Yahweh, cakes made from flour without leaven, and these only, being allowed. The regulation name for these "unleavened cakes" was matstsoth (Leviticus 10:12). Two exceptions to this rule should be noted (Leviticus 7:13; compare Amos 4:5):

"leavened bread" was an accompaniment of the thank offering as leavened loaves were used also in the wave offering of Leviticus 23:17. Rabbinical writers regularly use leaven as a symbol of evil (Lightfoot).

(3) In Teaching.

The figurative uses of leaven in the New Testament, no less than with the rabbins, reflect the ancient view of it as "corrupt and corrupting," in parts at least, e.g. Matthew 16:6 parallel, and especially the proverbial saying twice quoted by Paul, "A little leaven leaveneth the whole lump" (1 Corinthians 5:6; Galatians 5:9). But as Jesus used it in Matthew 13:33, "The kingdom of heaven is like unto leaven," it is clearly the hidden, silent, mysterious but all-pervading and transforming action of the leaven in the measures of flour that is the point of the comparison.